From c9ce233f0831118c6aa23197bad9ab07355a6ab6 Mon Sep 17 00:00:00 2001
From: Andrew Nicols <andrew@nicols.co.uk>
Date: Tue, 4 Nov 2025 09:16:22 +0800
Subject: [PATCH] MDL-87079 core: Call existing pcntl handlers

Whilst `register_shutdown_function` works as a queue, `pcntl_signal`
does not.

To preserve the behaviour of existing signal handlers, as are typically
found in CLI wrappers like PHPUnit and Behat, we should store any
existing handler
---
 lib/classes/shutdown_manager.php | 22 ++++++++++++++++++++--
 lib/upgrade.txt                  |  3 +++
 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/lib/classes/shutdown_manager.php b/lib/classes/shutdown_manager.php
index 5f0aec5dcf6..7642526cec4 100644
--- a/lib/classes/shutdown_manager.php
+++ b/lib/classes/shutdown_manager.php
@@ -39,6 +39,9 @@ class core_shutdown_manager {
     /** @var bool is this manager already registered? */
     protected static $registered = false;
 
+    /** @var array A list of pcntl handlers */
+    protected static array $pcntlhandlers = [];
+
     /**
      * Register self as main shutdown handler.
      *
@@ -58,8 +61,19 @@ class core_shutdown_manager {
         if (CLI_SCRIPT && extension_loaded('pcntl') && function_exists('pcntl_async_signals')) {
             // We capture and handle SIGINT (Ctrl+C) and SIGTERM (termination requested).
             pcntl_async_signals(true);
-            pcntl_signal(SIGINT, ['core_shutdown_manager', 'signal_handler']);
-            pcntl_signal(SIGTERM, ['core_shutdown_manager', 'signal_handler']);
+
+            $signals = [SIGINT, SIGTERM];
+
+            foreach ($signals as $signal) {
+                if (function_exists('pcntl_signal_get_handler')) {
+                    $handler = pcntl_signal_get_handler($signal);
+                    if (is_callable($handler)) {
+                        // We can restore the original handler later if needed.
+                        self::$pcntlhandlers[$signal] = $handler;
+                    }
+                }
+                pcntl_signal($signal, ['core_shutdown_manager', 'signal_handler']);
+            }
         }
     }
 
@@ -106,6 +120,10 @@ class core_shutdown_manager {
                 error_log('Exception ignored in signal function ' . get_callable_name($callback) . ': ' . $e->getMessage());
             }
         }
+        if (array_key_exists($signo, self::$pcntlhandlers)) {
+            $handler = self::$pcntlhandlers[$signo];
+            $handler($signo);
+        }
 
         if ($shouldexit) {
             exit ($exitcode);
diff --git a/lib/upgrade.txt b/lib/upgrade.txt
index dad08af27b6..c8759887258 100644
--- a/lib/upgrade.txt
+++ b/lib/upgrade.txt
@@ -1,6 +1,9 @@
 This files describes API changes in core libraries and APIs,
 information provided here is intended especially for developers.
 
+=== 4.1.22 ===
+* message: When responding to pcntl signals, call existing signal handlers.
+
 === 4.1.21 ===
 
 * Moodle's Behat `::execute()` method now supports the use of array callable syntax for calling other steps.